1. Field of the Invention
The present invention relates to an information-recording medium having, on a substrate, a recording layer capable of recording information, and a method for producing the same.
2. Description of the Related Art
In general, the optical information-recording medium (optical disk) capable of recording information only once by using the laser beam includes, for example, write-once type CD (so-called CD-R) and DVD-R. Such an optical information-recording medium is advantageous in that a small amount of CD""s can be commercially supplied to the market quickly at a convenient price as compared with the production of conventional CD (compact disk). The demand for such an optical information-recording medium is increasing in accordance with the recent popularization of personal computers or the like.
The optical information-recording medium of the CD-R type has a representative structure comprising a recording layer composed of an organic dye, a light-reflective layer composed of a metal such as gold, and a protective layer made of a resin which are stacked in this order on a transparent disk-shaped substrate having a thickness of about 1.2 mm (see, for example, Japanese Laid-Open Patent Publication No. 6-150371).
The optical information-recording medium of the DVD-R type has a structure comprising two disk-shaped substrates (having a thickness of about 0.6 mm) which are laminated with each other with respective information-recording surfaces disposed inwardly in an opposing manner. The optical information-recording medium of this type has such a feature that a large amount of information is recorded thereon.
Information is written (recorded) on the optical information-recording medium by radiating a near infrared laser beam (laser beam usually having a wavelength of about 780 nm in the case of CD-R or a wavelength of about 635 nm in the case of DVD-R). A portion of the dye recording layer, which is irradiated with the laser beam, absorbs the light, and its temperature is locally raised. As a result, a physical or chemical change (for example, generation of pit) takes place, and the optical characteristic is changed. Thus, the information is recorded.
On the other hand, information is also read (reproduced) by radiating a laser beam usually having the same wavelength as that of the recording laser beam. The information is reproduced by detecting the difference in reflectance between a portion (recorded portion based on the generation of pit) which has subjected to the change in optical characteristic of the dye recording layer and a portion (non-recorded portion) which is not subjected to the change.
In general, the disk-shaped optical information-recording medium, on which the information signal is recorded and reproduced by the aid of the light beam, includes read-only type optical disks referred to as so-called compact disk, write-once type optical disks capable of recording only once, and rewritable optical disks capable of not only reproduction but also recording and erasing of the information signal.
Polycarbonate resin or acrylic resin is generally used as a material for the substrate for the optical disk as described above. In view of the productivity, the substrate is produced by using the injection molding method or the injection compression molding method. After the molding treatment is applied, the substrate is cooled, and it is transported to the dye recording layer-forming step.
In the method for producing the optical information-recording medium as described above, when the recording layer based on the organic dye is formed on the substrate, the dye solution is applied onto the substrate while rotating the substrate. After the dye solution is applied, the clean air is allowed to flow toward the recording layer while rotating the substrate at a high speed so that the recording layer is dried.
In this case, when the intake for introducing the clean air is wide, a larger amount of clean air flows toward the outer circumferential portion of the recording layer as compared with the inner circumferential portion thereof. For this reason, the outer circumferential portion is dried without sufficiently blowing off the excessive dye solution, as compared with the inner circumferential portion. As a result, a problem arises such that the film thickness is non-uniform between the outer circumferential portion and the inner circumferential portion, and the recording characteristic is deteriorated.
In order to improve the throughput of the information-recording medium, the drying time is shortened by increasing the environmental temperature for drying the recording layer or the temperature of the substrate itself, rotating the substrate at a higher speed by increasing the concentration of the dye solution, or increasing the air blow speed during the drying. However, the method as described above involves such a problem that the running cost is expensive.
In the method for producing the optical information-recording medium as described above, two or more dye application mechanisms for forming the dye recording layer are installed for one molding machine for molding the substrate. That is, when two or more substrate-molding machines are installed, four or more dye application mechanisms are installed. The dye recording layer is hitherto formed with a plurality of production lines. For this reason, the maintenance cost for the respective equipments is expensive, and the quality control for each of the production lines is complicated, resulting in the large scale of the production equipment, and the enlargement of the installation space. In accordance therewith, it is feared that the price of the optical information-recording medium to be produced may become high, and the yield may be lowered.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide an information-recording medium and a method for producing the same which make it possible to reduce the drying time for a recording layer, obtain a uniform film thickness of the recording layer, and improve the throughput for the information-recording medium at low cost.
Another object of the present invention is to provide an information-recording medium and a method for producing the same which make it possible simplify the production line by satisfying a relationship of n/m less than 2 provided that m represents the number of substrate-molding machine or machines and n represents the number of dye application mechanism or mechanisms for forming a dye recording layer wherein the quality control is easily performed and the maintenance cost is reduced, making it possible to realize a small scale of the production equipment and reduce the installation space so that the low price of the information-recording medium produced thereby may be realized and the improvement in yield may be achieved.
According to the present invention, there is provided an information-recording medium comprising, on a substrate, a recording layer capable of recording information; wherein the recording layer is dried by rotating the substrate at a high speed and allowing clean air to flow through an intake which is formed to be narrow, toward the recording layer formed on the substrate.
According to another aspect of the present invention, there is provided a method for producing an information-recording medium comprising, on a substrate, a recording layer capable of recording information, the method comprising the step of drying the recording layer by rotating the substrate at a high speed and allowing clean air to flow toward the recording layer formed on the substrate; wherein an intake for introducing the clean air is formed to be narrow.
In the method for producing the information-recording medium described above, it is also preferable that the intake is narrowed by arranging a disk-shaped lid having an opening at least at a central portion, on the intake for introducing the clean air. Alternatively, the opening may have a wedge-shaped configuration or a substantially rhombic configuration.
It is also preferable that the lid has a first opening which has a large diameter disposed at a central portion, and it has a plurality of second openings which have diameters gradually decreased for those disposed in a direction toward an outer circumference in which a central angle resides in a spacing distance of not less than 10xc2x0.
It is also preferable that the lid is formed to have a substantially conical configuration which has a diameter continuously decreased downwardly, and it has an opening at a central portion. Alternatively, the lid may have a plurality of fins which are formed at a lower surface in which a central angle resides in a spacing distance of not less than 10xc2x0.
Accordingly, the clean air can be allowed to flow toward the entire surface of the recording layer substantially uniformly. Therefore, the recording layer can be dried uniformly concerning the planar direction and the film thickness direction of the recording layer. Thus, it is possible to produce the information-recording medium having good recording characteristics.
Further, the drying time for the recording layer can be shortened without increasing the environmental temperature for drying the recording layer or the temperature of the substrate itself, without rotating the substrate at a higher speed by increasing the concentration of the dye solution, or without increasing the air blow speed during the drying. Therefore, it is possible to remarkably suppress the increase in running cost. Further, it is possible to improve the throughput of the information-recording medium.
According to still another aspect of the present invention, there is provided an information-recording medium comprising, on a substrate, a dye recording layer capable of recording information; wherein the information-recording medium is produced by constructing a production line so that a relationship of n/m less than 2 is satisfied provided that m represents a number of molding machine or machines for molding the substrate, and n represents a number of dye application mechanism or mechanisms for forming the dye recording layer.
According to still another aspect of the present invention, there is provided a method for producing an information-recording medium comprising, on a substrate, a dye recording layer capable of recording information; wherein a production line is constructed so that a relationship of n/m less than 2 is satisfied provided that m represents a number of molding machine or machines for molding the substrate, and n represents a number of dye application mechanism or mechanisms for forming the dye recording layer. In this aspect, it is preferable that the production line is constructed by installing one dye application mechanism for forming the dye recording layer for one molding machine for molding the substrate.
Accordingly, it is possible to simplify the production line, and it is easy to perform the quality control for each production line. Further, the maintenance cost for each equipment can be reduced, making it possible to realize a small scale of the production equipment and reduce the installation space. Therefore, it is possible to realize the low price of the information-recording medium produced thereby, and it is possible to achieve the improvement in yield.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.